<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        ol li {
            /* 后代选择器 */
            color: red;
        }

        h2 {
            font-size: 10px;
            color: red;
        }

        .box {
            font-size: 20px;
            color: green;
        }

        #id {
            font-size: 30px;
            color: wheat;
        }

        /* 鼠标悬浮时 使用这个CSS */
        a:hover {
            color: greenyellow;
        }

        div {
            background-color: red;
            width: 200px;
            height: 200px;
        }

        .green-div {
            background-color: green;
            width: 200px;
            height: 200px;
        }
        .button1{
            background-color: rgb(200, 0, 0);
            height: 30px;
            width: 100px;
            border: none; /* 删除边框效果 */
            border-radius: 2px;
        }
        .button2{
            background-color: rgb(255, 255, 255);
            height: 30px;
            width: 100px;
            border-color: blue;
            /* border-radius: 2px; */
        }
        .button2{
            background-color: rgb(255, 255, 255);
            height: 30px;
            width: 100px;
            border-color: blue;
            /* border-radius: 2px; */
        }
    </style>
</head>

<body>

    <button class="button1">test1</button>

    <button class="button2">JOIN</button>

    <ol>
        <li>test</li>
    </ol>
    <hr>
    <span>标签选择器</span>
    <h2>选择器的开端1</h2>
    <h2>选择器的开端2</h2>
    <h2>选择器的开端3</h2>
    <hr>
    <h2 class="box">class选择器</h2>
    <h2 class="box">class选择器</h2>

    <h2 id="id">id选择器</h2>

    <a href="https://www.baidu.com" title="test">标签属性选择器</a>

    <hr>

    <div></div>
    <div class="green-div"></div>
    <div></div>


</body>

</html>